Flavonol Glucosides Research Articles

Distribution of Flavonols and Enzymes Participating in the Metabolism in Onion Bulbs: Mechanism of Accumulation of Quercetin and Its Glucosides in the Abaxial Epidermis.

Onion bulbs contain quercetin, quercetin 4'-glucoside (Q4'G) and quercetin 3,4'-diglucoside (Q3,4'G), almost all of which are localized in the abaxial epidermis of scales. There is a question of whether these compounds are synthesized in the abaxial epidermis or transported to the epidermis. To elucidate this, activities of enzymes that participate in the formation and degradation of quercetin glucosides were measured in the abaxial epidermis, adaxial epidermis and mesophyll. Activities of glucosyltransferases, which transform quercetin to Q4'G and Q4'G to Q3,4'G, were highest in the abaxial epidermis. Activity of phenylalanine ammonia-lyase was also higher in the abaxial epidermis than in other tissues. These results suggest that the flavonol glucosides are synthesized in the abaxial epidermis. Activities of glucosidases, which transform Q3,4'G to Q4'G and Q4'G to quercetin, were highest in the abaxial epidermis, suggesting that quercetin, which is present in the abaxial epidermis, is formed by deglucosidation of quercetin glucosides in the epidermal cells.

Seasonal accumulation of ultraviolet‐B screening pigments in needles of Norway spruce (Picea abies (L.) Karst.)

Conifer needles are highly effective in screening ultraviolet‐B radiation (280–320 nm). This ability is mainly attributed to the presence of flavonoids and hydroxycinnamic acids in the epidermal tissue. In two field cabinet experiments with two different clones of Norway spruce we assessed the seasonal accumulation of UV‐B screening pigments under near‐ambient, and close‐to‐zero UV‐B irradiation. At the beginning of needle development, i.e. in June, kaempferol 3‐O‐glucoside was the dominant UV‐B screening pigment. It was replaced during needle differentiation by the more effective diacylated flavonol glucosides, particulary kaempferol 3‐O‐(3",6"‐O‐di‐p‐coumaroyl)‐glucoside, which reached highest concentrations in July. In addition to the soluble pool of diacylated flavonol glucoside derivatives, a cell wall‐bound UV‐B screen in the epidermal cell walls was formed during needle differentiation, consisting mainly of p‐coumaric acid and kaempferol 3‐O‐glucoside. An effect of UV‐B radiation on the accumulation of diacylated flavonol glucosides was only observed in 1996 with clone 2, when the concentrations of kaempferol 3‐O‐(3",6"‐O‐di‐p‐coumaroyl)‐glucoside were significantly higher in July and August under field, and near‐ambient than under close‐to‐zero UV‐B irradiance. For wall‐bound p‐coumaric acid and kaempferol 3‐O‐glucoside UV‐B radiation enhanced the concentrations of these compounds by approximately 20% in relation to the concentrations in close‐to‐zero UV‐B‐treated plants in both field cabinet experiments.

Colouring agents in yellow and white flowered papaver radicatum in Northern Greenland

In the extreme north, Papaver radicatum s.l. occurs in a yellow and in a white-flowered type. The more severe the weather conditions the higher the frequency of the white phenotype. The colouring agents in the petals are all flavonol glucosides; in the yellow flowers gossypitrin (1) and herbacitrin (2), in the white ones the kaempferol glucoside astragalin (3). Only astragalin shows UV reflection, which is valuable in attracting insect pollinators, so very likely the presence of astragalin may be responsible for the success of the white-flowered type under suboptimal weather conditions. We were unable to confirm the hypothesis that the yellow colouring agents, gossypitrin and herbacitrin, should be more costly to produce than the white one, astragalin, as an investment in order to obtain the higher temperature observed in yellow flowers. The distribution pattern with high frequency of the yellow-flowered poppies where the likelihood of sunshine is high, may have other reasons than carbon allocation to the colouring agents. Yellow flowers are more showy than white ones, and although this in general benefits pollination it may also increase the risk of herbivory. White flowers are at the same time believed to escape herbivory and obtain a better pollination under dull weather conditions, due to the UV-reflection by astragalin.

Tautomerism of flavonol glucosides: relevance to plant UV protection and flower colour

The fluorescence emission spectra of the naturally occurring flavonoids, quercetin-7-glucoside, a 3′,4′-dihydroxyflavonol, and kaempferol-7-glucoside, a 4′-hydroxyflavonol, have been determined as a function of concentration in aqueous solutions. These spectra indicate that the extent of keto–enol phototautomerism in both flavonoids is greatest at high concentrations: a situation which favours molecules aggregation/dimerization. Such behaviour is consistent with phototautomerism being facilitated by a concerted, intermolecular transfer of protons between the partners in the flavonoid dimer. This excited state tautomerism dissipates absorbed energy harmlessly and as such provides a possible mechanism by which these molecules may function in the protection of plants from damaging UV radiation. The fluorescence excitation spectra of both kaempferol and quercetin-7-glucosides at high concentrations in aqueous solutions indicate the presence of significant amounts of the enolic tautomeric form in the ground-state. At lower concentrations only the kaempferol glucoside spectrum shows this. When kaempferol- and quercetin-7-glucosides were deposited on a cellulosic support, their reflectance and fluorescence excitation spectra could be resolved into contributions from keto and enol ground-state chromophores. The absorption of the enolic tautomer is at longer wavelengths (ca. 450 nm) than that of the keto tautomer (ca. 370 nm) and as it extends into the blue spectral region, would account for the yellow appearance of these flavonols in aggregation on cellulose and in concentrated solution in petal vacuoles.

Tissue and Spatial Distribution of Flavonol and Peroxidase in Onion Bulbs and Stability of Flavonol Glucosides during Boiling of the Scales

Two major flavonol glycosides [quercetin 3,4‘-diglucoside (F1) and quercetin 4‘-monoglucoside (F2)] and a flavonol aglycon quercetin were mainly localized in the abaxial epidermis of scales. Their contents increased on aging. Peroxidase in scales oxidized flavonols in the order quercetin ≫ F2 > isoquercetin ≫ F1, and the activity was higher in the outer than in the inner scales. These results suggest that the enzyme can participate in the formation of defense substances against infection and brown compounds in the dry skin from quercetin. Contents of F1 and F2 in scales were decreased by cooking by boiling. This decrease was due to the release of F1 and F2 into cooking water and their oxidation. F2 was oxidized more rapidly than F1 during cooking. The difference in the stability between F1 and F2 was due to the presence or absence of a hydroxyl group at the C-3 position of the glucosides. Keywords: Flavonols; peroxidase; distribution in tissues; thermostability; onion (Allium cepa)

Absorption and excretion of conjugated flavonols, including quercetin-4′-O-β-glucoside and isorhamnetin-4′-O-β-glucoside by human volunteers after the consumption of onions

Flavonols are polyphenols found ubiquitously in plants and plant-products. Flavonols, particularly quercetin, are potent antioxidants in vitro and their intake has been associated inversely with the incidence of coronary heart disease. The aim of this study was to investigate the accumulation in plasma and excretion in urine of flavonol glucosides following ingestion of lightly fried onions. Five healthy volunteers followed a low-flavonoid diet for 3 days. On day 4, after an overnight fast, subjects were given 300 g of lightly fried yellow onions which contain conjugates of quercetin and isorhamnetin, including quercetin-3,4′-diO-β-glucoside, isorhamnetin-4′-O-β-glucoside and quercetin-4′-O-β-glucoside. Blood collection was carried out at 0 min, 0.5, 1.0, 1.5, 2, 3, 4, 5 and 24h after the supplement. In addition, subjects collected all their urine for 24h following the onion supplement. Isorhamnetin-4′-O-β-glucoside and quercetin-4′-O-β-glucoside accumulated in plasma with maximum levels, defined as proportion of intake, of 10.7 ± 2.6% and 0.13 ± 0.03% respectively. The time of the quercetin-4′-glucoside peak plasma concentration was 1.3 ± 0.2 h after the ingestion of onions while a value of 1.8 ± 0.7 h was obtained for isorhamnetin-4′-glucoside. Excretion in urine, as a proportion of intake, was 17.4 ± 8.3% for isorhamnetin-4′-O-β-glucoside and 0.2±0.1% for quercetin-4′-O-β-glucoside. Possible reasons for the accumulation and excretion of isorhamnetin-4′-glucoside in proportionally much higher amounts than quercetin-4′-glucoside are discussed. It is concluded that flavonols are absorbed into the bloodstream as glucosides and minor structural differences affect markedly both the level of accumulation and the extent to which the conjugates are excreted.

Kaempferol 3- O-(6″-caffeoylglucoside) from Pteridium aquilinum

A new acylated flavonol glucoside from the aerial parts of Pteridium aquilinum was characterized as kaempferol 3- O- β-(6″-caffeoylglucoside) by chemical and spectral methods.

Effect of Storage and Domestic Processing on the Content and Composition of Flavonol Glucosides in Onion (Allium cepa)

The stability of the major flavonol glucosides, quercetin 3,4‘-O-diglucoside (QDG) and quercetin 4‘-O-monoglucoside (QMG), was studied in two varieties of onion (Red Baron and Crossbow) that were cured and stored for 6 months under normal commercial conditons and analyzed at regular intervals. Onions were also cooked by boiling in water and by frying in oil under normal domestic conditions. Apart from a 50% loss of quercetin 4‘-O-monoglucoside during the initial drying process, little change in content and composition was observed over 6 months of storage. Neither boiling nor frying resulted in interconversion of the quercetin conjugates or production of free quercetin, although a 25% loss overall was recorded for each process. Keywords: Onion; Allium cepa; flavonol; quercetin; glucoside; HPLC; storage; processing

UV-B induction of flavonoid biosynthesis in Scots pine (Pinus sylvestris L . ) seedlings

Cultivation of Scots pine (Pinus sylvestris L.) seedlings under simulated global radiation including the UV-B band (280 – 320 nm; 220 mW m–2 UV-BBE) led to increased formation of the diacylated flavonol glucosides 3″,6″-di-p-coumaroyl-astragalin and 3″,6″-di-p-coumaroyl-isoquercitrin in primary and cotyledonary needles, respectively. 3″,6″-Di-p-coumaroyl-astragalin was also the main constitutive diacylated flavonol glucoside in both needle types. This compound predominantly accumulated in primary needles upon UV-B irradiation, and reached concentrations of 2.4 μmol g–1 fresh weight (fw). Its concentration was only weakly affected in cotyledonary needles. 3″,6″-Di-p-coumaroyl-isoquercitrin was mainly induced in cotyledonary needles with maximum concentrations of 0.8 to 0.9 μmol g–1 fw, but was virtually unaffected in primary needles under the same irradiation conditions. Pulse labelling with L-(U-14C)phenylalanine revealed that these metabolites were formed de novo. Phenylalanine ammonia-lyase (EC 4.3.1.5) and chalcone synthase (EC 2.3.1.74) were only slightly induced by the UV-B treatment. The results described here represent the first report on UV-B-induced flavonoid biosynthesis in a conifer species.

Medicinal foodstuffs. V. Moroheiya. (1): Absolute stereostructures of corchoionosides A, B, and C, histamine release inhibitors from the leaves of Vietnamese Corchorus olitorius L. (Tiliaceae).

Three new ionone glucosides named corchoionosides A, B, and C were isolated from the leaves of Corchorus olitorius, commonly called "moroheiya" in Japanese, together with seven known compounds, an ionone glucoside (6S,9R)-roseoside, a monoterpene glucoside betulalbuside A, two flavonol glucosides astragalin and isoquercitrin, two coumarin glucosides scopolin and cichoriine, and chlorogenic acid. The absolute stereostructures of corchoionosides A, B, and C were determined by chemical and physiochemical evidence, which included the result of application of a modified Mosher's method, the CD helicity rule, and chemical correlation with (6S,9R)-roseoside. Corchoionosides A and B and (6S,9R)-roseoside were found to inhibit the histamine release from rat peritoneal exudate cells induced by antigen-antibody reaction.

Flavonoid in Fruits and Vegetables. Part II. Content of Flavonol Glucosides and Some Properties of Enzymes Metabolizing the Glucosides in Onion.

The contents of flavonol glucosides in yellow, red and white onions harvested in Hokkaido were measured. Seven varieties of yellow onion averaged 16.8mg/100g of quercetin-3, 4'-di-O-β-glucoside, 18.5mg/100g of quercetin-4'-O-β-glucoside, 0.8mg/100g of quercetin-3-O-β-glucoside and 2.9mg/100g of isorhamnetin-4'-O-β-glucoside. The red onion contained about 3-fold the amount of these glucosides while the white onion contained no detectable amounts of flavonols. The content of each flavonoid was higher in the outer scales than in the inner ones. Flavonol glucosidases and UDPG: flavonol glucosyltransferases were detected in the onions. The optimum pH of quercetin-3-O-β-glucosyltransferase, 4'-O-β-glucosyltransferase, 3-O-β-glucosidase and 4'-O-β-glucosidase was 6.0, 8.0, 4.5 and 7.0, respectively. In all the onion varieties, the activity of quercetin-4'-β-glucosyltransferase was higher than that of 4'-O-β-glucosidase, but the activity of 3-O-β-glucosyltransferase was lower than that of 3-O-β-glucosidase. Since quercetin-4'-O-β-glucosyl-transferase was not able to transglucosylate quercetin-3-O-β-glucoside and rutin, the precursor of quercetin-3, 4'-di-O-β-glucoside is estimate to be the 4'-O-β-glucoside and not the 3-O-β-glucoside.

Flavonol glucosides in pericarps of Zanthoxylum bungeanum

Two new flavonol glucosides, viz. quarcetin 3′,4′-dimethyl ether 7-glucoside and tamarixetin 3,7-bis-glucoside, together with hyperin, quercetin, quercitrin, foeniculin, isorhamnetin 7-glucoside, rutin, 3,5,6-trihydroxy-7,4′-dimethoxyflavone, arbutin, sitosterol β-glucoside, l-sesamin and palmitic acid were isolated from the pericarps of Zanthoxylum bungeanum. Their structures were established by spectroscopic and spectrophotometric methods.

Chemo‐enzymatic Synthesis of 6″‐O‐(3‐Arylprop‐2‐enoyl) Derivatives of the Flavonol Glucoside Isoquercitrin

AbstractA chemo‐enzymatic approach to some 6″‐O‐(3‐arylprop‐2‐enoyl) derivatives of the flavonol glucoside isoquercitrin (2a) was explored to overcome the inability to directly introduce these acyl moieties by an enzyme‐catalyzed reaction of 2a with the corresponding activated esters. This new approach was based on the regioselective introduction of a methyl malonate residue at the CH2OH of the sugar moiety by catalysis with the protease subtilisin (→ 22a). The mixed diester 22a was then subjected to chemoselective hydrolysis of the methoxycarbonyl function by another enzyme, biophine esterase (→ 23). Finally, the malonic monoester 23 was reacted in a Knoevenagel‐type condensation with benzaldehyde, 4‐hydroxybenzaldehyde, or 4‐hydroxy‐3‐methoxybenzaldehyde to afford the target 6″‐O‐(3‐arylprop‐2‐enoyl) isoquercitrins 2b–d.

Optimization of a quantitative HPLC determination of potentially anticarcinogenic flavonoids in vegetables and fruits

A rapid method based on RP-HPLC with UV detection is presented for the quantitative determination of five major flavonoid aglycons, viz. quercetin, kaempferol, myricetin, luteolin, and apigenin, in freeze-dried vegetables and fruits, after acid hydrolysis of the parent glycosides. Completeness of hydrolysis and extraction have been optimized by testing systematically different conditions such as acid concentration, reaction period, and methanol concentration in the extraction solution using samples containing various types of flavonoid glycosides. Optimum hydrolysis conditions are presented for flavonol glucuronides, flavonol glucosides, and flavone glycosides. Identity of the flavonoids was confirmed with diode array. Repeatability of the method was good, with coefficients of variation of 2.5-3.1% for quercetin, 4.6-5.6% for kaempferol, 4.6% for myricetin, 3.3% for luteolin, and 2.8% for apigenin. CV of the within-laboratory reproducibility was less than 2 times the CV of repeatability. Recoveries of the flavonols quercetin, kaempferol, and myricetin ranged from 77 to 110%, and recoveries of the flavones apigenin and luteolin ranged from 99 to 106%. The method presented allows a fast, quantitative, and reproducible determination of five flavonoids in freeze-dried foods

Isolation and Characterization of a UDPGlucose: Flavonol O3-Glucosyltransferase from Illuminated Red Cabbage (Brassica oleracea cv Red Danish) Seedlings

A UDPGlc:flavonol O(3)-glucosyltransferase (EC 2.4.1.91) that catalyzes the formation of quercetin and kaempferol O(3)-glucosides has been purified about 1450-fold from illuminated red cabbage (Brassica oleracea cv Red Danish) seedlings with a 3.3% yield. Purification of the enzyme was achieved by (NH(4))(2)SO(4)-precipitation, gel-filtration, ion-exchange chromatography on DEAE-Bio-Gel and Q-Sepharose, chromatofocusing, and electrophoresis in nondenaturing polyacrylamide (10%) gels. The enzyme preparation had a pH optimum between 5.8 and 6.2, isoelectric point in the pH range 4.25 to 4.55, a M(r) of 59,000, and it was composed of two similar subunits of M(r) 29,500. The glucosyltransferase reached half substrate saturation at 180 micromolar (UDPGlc) and 7 micromolar (quercetin) concentrations. Kaempferol, which was glucosylated at a relative rate of 87%, had a lesser affinity for the enzyme (K(m)~12 micromolar). Flavanones, flavanols, flavones, dihydroflavonols, and anthocyanidins were not readily utilized as substrates, suggesting that the enzyme is specific for flavonol glucoside biosynthesis.

6-Hydroxyflavonol glycosides from Chrysactinia mexicana

Four flavonol glucosides were extracted from aerial parts of Chrysactinia mexicana after elimination of exudate flavonoids. They were identified as quercetagetin-3-glucoside, quercetagetin-7-glucoside, 6-hydroxykaempferol 7-glucoside 6-hydroxykaempferol 7-acetylglucoside. 6-Hydroxykaempferol 7-glucoside is a very rare flavonol, while its acetyl derivative is a new natural product. The exudate flavonoids encountered in this plant are methylated aglycones based on the same flavonols.

Characterization of the flavonol glycosides in Petunia

The flavonol glycosides from 17 different Petunia hybrida cultivars and species were characterized. Fourteen different flavonol glucosides were identified. Eight of these glucosides have not previously been reported for Petunia. They are quercetin and kaempferol 3-glucoside, 3,7-diglucoside, 3-caffeoylsophoroside and 3-caffeoylsophoryl-7-glucoside. A tentative flavonol glucoside biosynthetic pathway is proposed.

Enzymatic synthesis of polymethylated flavonols in Chrysosplenium americanum: III. Purification and kinetic analysis of S-adenosyl- l-methionine:3-methylquercetin 7-O-methyltransferase

An O-methyltransferase (OMT) which catalyzes the methylation of 3-methylquercetin to 3,7-dimethylquercetin, the second step of methyl transfers toward the biosynthesis of polymethylated flavonol glucosides, has been isolated from Chrysosplenium americanum shoot tips. The 7-OMT was purified by ammonium sulfate precipitation, gel filtration, chromatofocusing and ion-exchange chromatography using a fast protein liquid chromatography system. Compared with previously reported methods ((1985) Arch. Biochem. Biophys. 238, 596–605), this protocol resulted in a highly purified enzyme preparation, free from other OMT activities, which allowed the study of its kinetic mechanism. Substrate interaction and product inhibition patterns obtained were consistent with an ordered bi bi mechanism, where S-adenosyl- l-methionine is the first substrate to bind to the enzyme and S-adenosyl- l-homocysteine is the last product released. However, the results obtained did not exclude the formation of one or more dead-end complex. The similarity in kinetic characteristics of this enzyme to those of the other Chrysosplenium OMTs suggests that methyltransferases of this tissue may have evolved from a common precursor.

Tissue culture of Chrysosplenium americanum and its potential for flavonoid production

Chrysosplenium americanum (Saxifragaceae) accumulates a variety of partially O-methylated flavonol glucosides. Because of the semi-aquatic nature of this plant and its extensive contamination with endogenous organisms, the initiation of shoot and callus cultures could only be achieved after (a) using a special surface sterilization procedure, (b) production of new shoots from initial explants, and (c) selective elimination of organogenic structures during several subcultures. HPLC analysis of the cultured tissues established the presence of a number of flavonoids characteristic of the intact plant, though in lower and variable concentrations. However, shoot and callus cultures exhibited flavonoid profiles similar to those of the intact leaves and roots, respectively.

Studies on the antihemorrhagic substances in herbs classified as hemostatics in Chinese medicine. IX. On the antihemorrhagic principles in Typha lactifolia L.

By following the antihemorrhagic activity according to Tajima's method, two antihemorrhagic principles, a new flavonol glucoside (1) and an unknown compound (2), were isolated from the dried pollen of Typha lactifolia L., which is one of the most important herbs for treatment of stagnant blood and bloody stools in traditional Chinese medicine.The structure of 1 was established as isorhamnetin 3-rutinoside-7-rhamnoside (3-[6-O-(6-deoxy-α-L-mannopyranosyl)-β-D-glucopyranosyl] Oxy-5-hydroxy-7-[β-L-mannopyranosyl] oxy -2-(4-hydroxy-3 -methoxyphenyl)-4H-1-benzopyran-4-one), based on chemical transformations and spectral data.